Heretofore, as a load resistor to be used in load characteristic tests of a power generator, that which employs a high-voltage resistor element 1′ having a fin 9 as shown in FIG. 3 has been utilized. In the same figure, numeral 2′ denotes an outer tube in a cylindrical shape, which is formed to be approximately 1 m long.
And numeral 3 denotes a resistive heat-generating wire; 4 an electrode rod; and 5′ an insulating material filling up the space between the resistive heat-generating wire 3 with the electrode rod 4 and the internal surface of the outer tube 2′, and hermetically sealed with an end sealing member 6. This insulating material 5′ is in a powdery state, and has a function of insulating the outer tube 2′ from the resistive heat-generating wire 3 with the electrode rod 4.
Numeral 7 denotes a connection terminal, which is sandwiched and fixed on both sides by nuts 8, 8 screwed onto an outer end threaded portion 4a of the electrode rod 4. And through the connection terminal 7, the high-voltage resistor element 1′ is connected to another adjacent one. Numeral 9 denotes the fin as mentioned above, which functions as a heatsink to radiate the heat generated when the resistive heat-generating wire 3 is energized. The fin 9 is formed integrally with, or mounted onto the circumference of, the outer tube 2′ in a spiral shape with a spacing of approximately 7 mm along its longitudinal direction.
To accommodate the operating voltage of 6,600 V, this high-voltage resistor element 1′ is specified to have a rated voltage of 400 V and a dielectric strength of 2,000 V for 1 minute.
FIG. 4 shows a high-voltage resistor circuit 10 in which the high-voltage resistor elements 1′ are connected in series. Numeral 11 denotes a connection member, which connects the adjacent high-voltage resistor elements 1′ to each other in place of the connection terminal 7. Numeral 12 denotes a rectangular frame in a box shape, and between arrangement boards 12a′ of this rectangular frame 12, both ends of ten (10) high-voltage resistor elements 1′ are penetratingly bridged to form the high-voltage resistor circuit 10.
FIG. 5 shows a schematic configuration of a high-voltage load resistor unit 13. In the high-voltage load resistor unit 13, the above-mentioned high-voltage resistor circuits 10 are bridgingly housed in multiples of fifteen (15) columns. In this case, the high-voltage resistor elements 1′ are disposed alternately so that the fins 9 of the high-voltage resistor elements 1′ do not overlap one upon another. This is because, when each of the high-voltage resistor elements 1′ is energized, extremely high heat is generated, and thus air cooling must be uniformly provided by a cooling fan from bottom to up.
FIG. 6 shows a practical example in which the high-voltage load resistor unit 13 is provided with a cooling fan 14. In the same figure, numeral 15 denotes a vibration-proof rubber, and 16 an insulator. By additionally providing this insulator 16, the function that further increases the ensured insulation is obtained. In the figure, numeral 17 denotes a hood, and 18 an installation base.
Here, the references in the prior art are given as follows:                Japanese Patent Laid-open No. 9-15307        Japanese Patent Laid-open No. 9-15308        Japanese Patent Laid-open No. 2000-19231        
As a result of conducting the load characteristic tests of the high-voltage power generator with use of the conventional dry-type high-voltage load resistor unit 13 such above, it has been found that the temperature of the high-voltage load resistor unit 13 as air-cooled has risen to 140 degrees C. as a whole, and that of the high-voltage resistor element 1′ as a unit has risen to 350 degrees C. to 700 degrees C.
This is because, if the fins 9 of the high-voltage resistor elements 1′ arranged in the high-voltage resistors circuit 10 are disposed alternately so that they are not overlapped, the form of this fin 9 provides a resistance to the ventilation by the cooling fan 14, which causes the heat to be confined to within the rectangular frame 12, and thus the effect on the cooling performance of the cooling fan 14 is not sufficiently obtained. The fin 9, which is habitually provided for the high-voltage resistor element 1′ of this kind, is extremely effective for use in a low-voltage resistor element, however, it has not been elucidated that the fin 9 causes various detrimental effects as described below.
Specifically, because the fin 9 provides a resistance to the ventilation, an air turbulence and a disturbed air stream are produced in the high-voltage load resistor unit 13, and thus the vibration phenomena that occur as a result thereof is unavoidable. In the prior art example, this phenomena is avoided by use of the vibration-proof rubber 15, however, the hazard in the tests cannot yet be eliminated.
Moreover, because the insulating material 5′ hermetically sealed in the outer tube 2′ of the high-voltage resistor element 1′ is in a powdery state, it shifts to one side by such an external force vibration, which results in the impossibility of realizing a uniform thickness covering and the partial insufficiency of the insulation, and finally acts as a trigger for a dielectric breakdown. In addition, because of the powdery state, the resistive heat-generating wire 3 being red hot in operation can easily burnout or disconnect by the vibration, which results in the lack of a heat resistance. Nevertheless, the cause of troubles, which was often brushed off as an erroneous operation made by the operator, has not been thoroughly elucidated.
Furthermore, because the form of the fin 9, which is designed for the heat radiating effect, is tipped, when the voltage is raised, sharp edges 9a, 9a, . . . (see FIG. 3) initially generate corona discharges and finally generate arc discharges with the rectangular frame 12, which result in dielectric breakdown. This fact has been found finally as a result of experiments conducted over many years. Thus, with the conventional high-voltage resistor element 1′, it has been impossible to carry out the load characteristic tests without involving hazard.
As a safety measure against the dielectric breakdown resulting from the arc discharges, the insulator 16 is provided, however, because there is no place for high-voltage overcurrent to escape, the entire high-voltage load resistor unit 13 can be burnt down, and because of this hazard, the operator could not come near to it during the operation.
In addition, the fin 9 makes it difficult to see inside the rectangular frame 12 from above, which presents an interference in maintenance, inspection and adjustment, and further, because only the burnt or disconnected high-voltage resistor element 1′ cannot be laterally extracted from the rectangular frame 12, a partial replacement could not be carried out on the working site. And every time there arose the need for the partial replacement, the entire high-voltage load resistor unit 13 had to be brought back to the plant for removing the other high-voltage resistor elements 1′ before carrying out the required partial replacement, which causes the interruption and postponement of the load characteristic tests.
Here, the major objects of the present invention to be achieved are as follows:
Specifically, a first object of the present invention is to provide a high-voltage resistor element which can withstand the temperature rise due to the heat generated in conducting load characteristic tests of a high-voltage power generator.
A second object of the present invention is to provide a high-voltage resistor element for use in a high-voltage load apparatus which is to be free from dielectric breakdown even at a high voltage.
A third object of the present invention is to provide a high-voltage resistor element which is superior to vibration resistance due to air cooling. highly durable
A fourth object of the present invention is to provide a high-voltage resistor element which can be easily extracted one by one from a supporter and accordingly has advantageous to maintenance, inspection, adjustment, replacement and repair.
A fifth object of the present invention is to provide a high-voltage resistor element which is lightweight and compact.
Other objects of the present invention will be naturally apparent from the description, drawings, and especially the claims.